CVE-2009-4455 in ASA 5500
Summary
by MITRE
The default configuration of Cisco ASA 5500 Series Adaptive Security Appliance (Cisco ASA) 7.0, 7.1, 7.2, 8.0, 8.1, and 8.2 allows portal traffic to access arbitrary backend servers, which might allow remote authenticated users to bypass intended access restrictions and access unauthorized web sites via a crafted URL obfuscated with ROT13 and a certain encoding. NOTE: this issue was originally reported as a vulnerability related to lack of restrictions to URLs listed in the Cisco WebVPN bookmark component, but the vendor states that "The bookmark feature is not a security feature."
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Analysis
by VulDB Data Team • 12/18/2017
The vulnerability described in CVE-2009-4455 represents a critical configuration flaw in Cisco ASA 5500 Series Adaptive Security Appliances running specific software versions. This issue stems from the default configuration settings that fail to properly enforce access controls for portal traffic, creating an unintended pathway for authenticated users to bypass established security boundaries. The vulnerability specifically affects ASA versions 7.0, 7.1, 7.2, 8.0, 8.1, and 8.2, indicating a widespread impact across multiple release branches of the security appliance platform.
The technical exploitation mechanism relies on manipulating URL parameters through ROT13 obfuscation combined with specific encoding techniques to craft malicious requests that can traverse the security appliance's intended access controls. This allows remote authenticated users to access backend servers that should otherwise be restricted, effectively bypassing the WebVPN bookmark component's access restrictions. The vulnerability demonstrates a fundamental flaw in how the appliance processes and validates URL requests, particularly when these requests contain encoded or obfuscated elements that can circumvent standard validation mechanisms. According to the vendor's assessment, the bookmark feature itself is not considered a security feature, which suggests that the vulnerability stems from improper handling of user input rather than a deliberate security weakness in the bookmark functionality.
The operational impact of this vulnerability extends beyond simple unauthorized access to potentially enabling more sophisticated attacks. An authenticated attacker could leverage this flaw to access internal web applications, databases, or other backend systems that are typically protected by the security appliance's access controls. This represents a significant elevation in privilege and could potentially lead to data exfiltration, system compromise, or further lateral movement within the network infrastructure. The vulnerability's exploitation requires only remote authenticated access, making it particularly dangerous as it can be triggered by users who already have legitimate access to the system. This issue directly relates to CWE-285, which addresses improper authorization in security appliances, and aligns with ATT&CK technique T1071.004 for application layer protocol usage.
Mitigation strategies should focus on implementing proper access control configurations that enforce strict validation of URL parameters and prevent the bypass of security boundaries through encoded or obfuscated requests. Network administrators should ensure that all ASA appliances are updated to the latest software versions that address this vulnerability, as the vendor has likely released patches to correct the improper URL handling behavior. Additionally, implementing network segmentation, enhanced logging, and monitoring for suspicious URL patterns can help detect potential exploitation attempts. The configuration should explicitly disable or restrict the WebVPN bookmark feature if it's not required, and all access controls should be reviewed to ensure that backend server access is properly restricted based on user roles and permissions. Organizations should also consider implementing web application firewalls or additional security controls that can detect and block ROT13 encoded or other obfuscated URL patterns that attempt to exploit similar vulnerabilities.